So, I live in Wi, and last night was our first measurable snowfall. I have a 98 LT Blazer 4x4 AT, and it didnt seem to handle all that great in 4HI. This morning, I jacked it up and ran it in Drive in 4HI, the rear drivers side wheel was spinning but thats it. The driveshaft to the front axle was spinning but the tires were not. So looks like my 4HI isnt working or what???

 

Probably the 4wd vacuum actuator. Do you hear a clunk from the transfer case when you shift to 4hi/lo?

 

I used to, I have had the truck since last April, blew the transmmission out, and replaced it. The 4x4 worked then, but maybe something came unplugged when I swapped the trans??

 

Ok, I think I have the problem solved. The vacuum plug that plugs into to the top of the transfer case must have been put back in (by me) the wrong way. Now, should the vac line at the accumlator have constant sucction on it, and does what I describe sound like what the problem was, is??

 

Yup, mine was doing the same thing. Replaced the actuator, and its all good. It is located under your battery holder, not much to replacing it, but the little bugger costs about $200

 

The actuator? $200? Hardly... MSRP for the vacuum actuator from the dealer is $86 with many online GM parts dealers selling it for $60.

 

Well, I wish the price was the same here, in Regina. Had to buy it right from GM, cause nobody had the part, they charged me 200 bones. But I thought , what the heck, no fun having a 4X4 with only rear wheel drive!

 

I was just at the dealer today and the actuator thast is mounted on the firewall is the $80 dealer part, the "servo" is the part under the battery tray and that is $160 at the delaer here in IL. I found the actuator at GMPARTSDIRECT.COM for roughly $50 shipped, hope this fixes my problem.

 

The vacuum switch on the firewall was $56 (I replaced it 2 weeks ago in the hopes that it was my problem). The device under the battery tray was $86, exactly as swartlkk said.

 

Do you have the part number for the actuator under the batttery tray? Also I had the battery tray out last night and there was a spring that appeared not connected to anything, do you know if the spring is to hold the dust boot on the shaft or is it for something else. I don't think my problem is with tghe vacumn switch or actuator as I now can get the truck into auto, 4Hi and 4lo buty requires a combination of pushing different buttons. to get in auto requires 2hi + auto button, to get out of auto requires 4lo + 2hi. 4lo engages with solo 4lo button to get out requires 4lo+2hi, very weird.